Objective: To study how the concentrations of proteoglycans (PGs) and collagen change in various parts of tibial articular cartilage during aging, and to evaluate the development of spontaneous osteoarthrosis (OA) in guinea pigs.
Methods: PGs were extracted from guinea pig cartilage samples using 4M guanidine hydrochloride, and the amount of hydroxyproline was determined in the extraction remainder. The molecular size and aggregation of PGs were analyzed by electrophoresis, and the glycosaminoglycan composition was assessed by high-performance liquid chromatography.
Results: The PG concentration was proportional to the load distribution. However, when OA became histologically manifest, the PG concentration decreased by 50% (from a mean of 44 microg to 22 microg per mg fresh tissue) and the collagen level decreased by 40% (from a mean of 17 microg to 10 microg per mg fresh tissue), while the proportion of water increased by 13% (from a mean of 710 mg to 800 mg per mg fresh tissue).
Conclusion: Unmineralized cartilage can, within physiologic load limits, respond to increased mechanical demands by increasing the PG and collagen concentrations. Beyond a certain limit, however, the cartilage can no longer compensate for further increases in stress, which results in cartilage degeneration and losses of matrix constituents. These losses seemed to appear earlier in the disease process than has been described in previous animal models of secondary OA.